Borrelia miyamotoi Transmission: Larval Deer Ticks Can Infect
Borrelia miyamotoi transovarial transmission changes how we think about larval deer ticks.
In Lyme disease, larval ticks are typically not infected with Borrelia burgdorferi because the bacteria are not usually passed through tick eggs.
But Borrelia miyamotoi is different.
Researchers have shown that infected adult ticks can pass B. miyamotoi to their offspring through transovarial transmission, meaning larval ticks may already carry infection when they hatch.
What Borrelia miyamotoi Transovarial Transmission Means
According to investigators from the Centers for Disease Control and Prevention, larval ticks can already be infected with Borrelia miyamotoi after they hatch.
This occurs through transovarial transmission, a process in which an infected adult female tick passes the bacteria to offspring through infected eggs.
This is clinically important because larval ticks are often assumed to be harmless compared with nymphal ticks.
That assumption may not hold for B. miyamotoi.
CDC Study on Larval Tick Transmission
Researchers infected experimental mice with Borrelia miyamotoi, the relapsing fever bacterium.
They found that “minimal or partial blood meals by single-feeding transovarially B. miyamotoi-infected larvae also resulted in approximately half of experimental hosts developing infections detectable by examination of blood for presence of B. miyamotoi DNA,” writes Breuner from the CDC’s National Center for Emerging and Zoonotic Infectious Diseases.
This finding challenges the assumption that larval ticks are always low risk.
Why Larval Deer Ticks Pose a Unique Risk
Larval ticks are extremely small and easy to miss.
They are often active in July and August, when many people are outdoors and may be less vigilant about tick protection.
Public health messaging has traditionally emphasized nymphal ticks in spring and early summer.
However, this study suggests that late-summer exposure may also carry risk when larval ticks are infected with B. miyamotoi.
How This Differs From Lyme Disease
In Lyme disease, larval ticks are generally not considered an important source of infection because Borrelia burgdorferi is not typically transmitted through eggs.
By contrast, B. miyamotoi can be passed from infected female ticks to offspring.
This distinction matters for prevention, diagnosis, and patient education.
Patients bitten by larval ticks may still need monitoring for symptoms of tick-borne coinfections and relapsing fever–type illness.
Public Health Implications
The authors suggested that public health officials consider revising tick bite prevention messaging to include larval ticks and their seasonal activity.
This is especially important in July and August, when larval ticks may be active and people may mistakenly assume the highest-risk season has passed.
Prevention messages should include daily tick checks, protective clothing, repellents, and awareness that very small ticks can still matter clinically.
Clinical Takeaway
Larval deer ticks can transmit Borrelia miyamotoi when they acquire infection through transovarial transmission.
This expands the clinical importance of larval tick bites and late-summer tick exposure.
Patients and clinicians should not assume that larval ticks are harmless, particularly when symptoms follow a summer tick bite.
Related Articles
Borrelia miyamotoi
Larval Ticks May Be a Threat After All
Study Demonstrates Larval Ticks May Be a Threat
Prevention of Lyme Disease
Lyme Coinfections
References
- Breuner NE, Hojgaard A, Replogle AJ, Boegler KA, Eisen L. Transmission of the relapsing fever spirochete, Borrelia miyamotoi, by single transovarially-infected larval Ixodes scapularis ticks. Ticks Tick Borne Dis. 2018.
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
Lone Stars also transmit some infections transovarially.
So if you have had chiggers could you have lyme or another tick borne illness?
No. I posted an story about the association of a chigger bite with alpha-gal allergy (red meat allergy). These stories will hopefully trigger further research. You can read the story I posted at https://www.facebook.com/plugins/post.php?href=https%3A%2F%2Fwww.facebook.com%2Fdanielcameronmd%2Fposts%2F2204587233160186
Hi Dr. Cameron, I know this article is from a few years back, but thought I’d try my luck in getting in touch with you! Do you know what percentage of larval ticks are suspected of being infected with borrelia miyamotoi in states like CT? Thank you!
I have not seen any information on how often Larval ticks harbor B. miyamotoi or B. burgdorferi.
Thank you!
Hi Dr Cameron,
Can a larvae deer tick transmit Lyme disease to a human? Thanks so much
Transovarially transmission has been considered in tick borne disease, that is the infection passes through the egg to the larva. I have not seen much research in this area.
Hi Dr. Cameron,
I believe I have been bitten by a larval deer tick. (viewed under microscope, six legs, all mouth “prongs” intact. I recently finished a two week course of Doxycycline for an infected lone star tick bite. I removed the larval tick two days ago, and I believe I caught it well less than 24 hours after attaching, though I can’t be sure. I was given Doxycyline from my dermatologist for prophylaxis. He said I should take one 100mg pill. Do you think this is necessary for a larval tick bite that is not infected, or is this not enough and I should look into another full course of Doxy? Obviously I need to do a better job protecting myself in the future. Thanks in advance.
The prophylaxis dose should have been 200 or two 100 tablets. I am not supportive of a single dose prophylaxis approach. Read my perspective.vv https://danielcameronmd.com/perspective-dont-trust-single-dose-doxycycline-to-prevent-lyme-disease/
There has been no study of prophylaxis for a larval tick.
Thank you, I chose not to take the medication in this case. I did not identify the tick properly, either. Upon turning it over and looking closer, I actually think it may be a nymph, unfortunately. Either a lone star or deer tick nymph. I am caring for the bite site carefully, and have chosen to do “watchful waiting.” I have no idea if I’m doing the right thing. I don’t know if jumping into another several weeks of Doxycyline therapy after just completing two weeks is a good idea, either. I am located in central NC.